1. Field of the Invention
The present invention relates to a direct-type back light module, a diffuser plate and a method of fabricating the same. More particularly, the present invention relates to a direct-type back light module, a diffuser plate with enhanced transmittance and a method of fabricating the same.
2. Description of Related Art
Recently, along with the enhancement of the performance of the computer and the development of internet and the multimedia technology, the transmission of the image information has progressed from analog transmission to digital transmission. In order to meet the need of the consumers, the size of the video or image device should be smaller, thinner and lighter. Even though the performance of the conventional cathode ray tube (CRT) display is widely acceptable, however, the size of the electron tube of the CRT display is huge, besides the radiations emitted from the CRT display is a health concern. Therefore, with the development of the optoelectronic and semiconductor technology, the flat panel display (FPD) such as liquid crystal display (LCD), organic electroluminescence display (OELD) or plasma display panel (PDP) has gradually become the main stream of the display.
In general, the LCD may be classified into reflective-type LCD (reflective LCD), transmission-type LCD (transmissive LCD) and semi-transmissive semi-reflective LCD according to the light source thereof. For example, the transmissive LCD or the semi-transmissive semi-reflective LCD is mainly constructed from a liquid crystal panel and a back light module. The liquid crystal panel is constructed from two layers of transparent substrate and a liquid crystal layer disposed between the two transparent substrates. The back light module is adopted for providing the surface light source of the liquid crystal panel.
FIG. 1 is a schematic cross-sectional view and an enlarged local view of a conventional direct-type back light module. Referring to FIG. 1, the direct-type back light module 100 includes a lamp box 110, a plurality of cold cathode fluorescence lamp (CCFL) tubes 120 and a diffuser plate 130. The material of the lamp box 110 includes light reflective material. Therefore, most of light emitted from the cold cathode fluorescence lamp tubes 120 be used by the LCD. In addition, the cold cathode fluorescence lamp tubes 120 are arranged with mutually applicable intervals. Therefore, the brightness of the surface light source between two adjacent cold cathode fluorescence lamp tubes 120 is lower. Since the uniformity of the light source of the back light module is important, thus, the diffuser plate 130 is disposed on the light outputting plane of the direct-type back light module 100.
Generally, in the conventional technology, in order to render the diffusion of the light via the diffuser plate 130 is uniform, a plurality of diffusion particles 132 are doped in the diffuser plate 130. However, the transmittance of the diffusion particles 132 used in the conventional technology is bad, and the conventional diffusion particles 132 is of optically lower transmittance than that of the air medium. Therefore, the overall transmittance of the diffuser plate 130 is reduced, and the brightness of the surface light source provided by the direct-type back light module 100 is also reduced. In order to resolve the problem of reduction in the brightness of the surface light source provided by the direct-type back light module 100, a prism film 140 is disposed in the direct-type back light module 100 in a conventional technology. However, this increases the costs. Therefore, how to prevent the reduction of the transmittance due to the diffusion particles 132 and to enhance the brightness of the surface light source provided by the direct-type back light module 100 is an important issue.
Moreover, in the conventional technology, the diffuser plate 130 is mechanical structurally weak, and the doped diffusion particles 132 are highly hygroscopic. Therefore, when the diffuser plate 130 expands due to heat and/or absorption of moisture under certain circumstances, the warping of the diffuser plate 130 due to a weak mechanical structure would easily occur.
In addition, in the conventional technology, diffuser plate 130 is manufactured by first forming a large mother plate (not shown), and then the mother plate is cut by using a computer numerical control (CNC) machine to obtain a plurality of diffuser plates 130. However, the use of CNC machine for fabricating the diffuser plates 130 could be expensive, and the efficiency of cutting of the mother plate is low and not effective.